1. Purpose of the Invention
This invention relates to certain new and useful improvements in generators for use with loads having changing impedance characteristics and method of use therefor, and, more particularly, to generators which have power outputs with impedance to match the impedance characteristics of the loads and which loads which may be in the form of ionic conduction lamps.
2. Brief Description of the Prior Art
For many years, ionic conduction lamps, including phosphor excitable lamps, have been used, and have replaced the conventional incandescent lamps in many applications. Phosphor excitable lamps include, for example, the well-known fluorescent lamp and similar gaseous discharge lamps, and the more recent electroluminescent lamp, sometimes referred to as a "cathode discharge lamps".
Phosphor excitable lamps operate on the principle of generating ultraviolet radiation by charging a gas, such as mercury, with electrons, and energizing or exciting the phosphors included in a phosphor coating in the lamp to produce visible light. In most conventional fluorescent lamps and similar gas discharge lamps, the lamp includes a hot cathode located on the interior thereof and connected to electrodes on the exterior of the lamp. In the electroluminescent lamp, a capacitive effect is achieved with a phosphor coating on a transparent sheet and with a second electrode being comprised of an aluminum or similar metal sheet. Other forms of ionic conduction lamps include for example, the metal vapor lamps e.g., the sodium vapor lamps and the mercury vapor lamps. These lamps also operate on the basis of generating an ionic current flow, much in the same manner as the phosphor excitable lamps.
These ionic conduction lamps are operable in conjunction with any of a number of conventionally known ballasts. The ballast is generally a series reactor transformer which includes a large number of windings. Thus, the ballast acts as an inductive device to increase the voltage for igniting the ionic conduction lamp. The ballast primarily serves to both ignite the lamp and to also limit the current to the lamp. Immediately after the lamp is ignited, the impedance of the lamp drops to a very low level and, hence, it is necessary to limit the current after ignition in order to avoid burning-up the lamp. The inductive reactance in the conventional ballast operates to limit the current after ignition of the lamp.
There are many disadvantages of the conventional ballast system used in connection with ionic conduction lamps. One of the disadvantages lies in the weight and size factor of the conventional ballast. Due to the heavy transformer, provision must be made in each conventional lamp fixture in order to mount and support the weight of the ballast. Moreover, if they are used for any excessive period of time, the ballast may heat up and may tend to burn out thereby necessitating replacement.
In addition to the above, these conventional ballasts utilize low frequency operation, as for example, 60 Hz power. Moreover, by virtue of the construction of the conventional ballasts, they are typically not adaptable for high-frequency operation. The transformer core in the ballast often tends to vibrate and generate a hum in the audible frequency spectrum. While this hum may not have a great amplitude, it is, nevertheless, distracting and uncomfortable.
Another disadvantage of the conventional ballast is that large capacitors are oftentimes required to correct the power factor and phase displacement. These capacitors are relatively expensive due to their size and thus substantially increase the overall cost of the ballast. Even moreso, the use of an inductive device of this type often generates a significant amount of heat. In many cases, where the lamp is not mounted in an environment where air flow can dissipate the heat, other means must be employed to dissipate the heat generated by the ballast.
One of the significant disadvantages of conventional ballasts, at least in present energy shortage times, is that the ballast requires a substantial amount of electrical power for its operation in order to ignite and thereafter maintain energization of the lamp. A substantial amount of power is required to ignite the ionic conduction lamp and after the lamp has been ignited, a lesser but continuing current source is applied to the two electrodes of the lamp in order to maintain energization thereof.
There have been several proposed high frequency operating devices which employ both an inductor and a transistor for purposes of operating fluorescent lamps. For example, U.S. Pat. No. 3,396,307 to Campbell discloses an inverter circuit operating a fluorescent lamp from a direct current source. A shunt capacitor is also used and is connected across a secondary coil of a transformer for load regulation when excessively high voltage conditions might be incurred. U.S. Pat. No. 3,889,153 to Pierce also discloses a power source for operating fluorescent lamps and similar lamps at a frequency of 20,000 hertz. In addition, U.S. Pat. No. 4,005,335 to Perper discloses another form of power source similarly provided for operating fluorescent lamps at a frequency of 20,000 hertz.
It has been found by use of the generator of the present invention, that it is possible to maintain energization of the lamp and obtain the same light output as a lamp operated with a conventional ballast, but with lesser power consumption; or otherwise to obtain a greater light output as a lamp operated with a conventional ballast with only the same power consumption.